Light valve



p 1 o. o. CECCARI'NI 1,855,623

LIGHT VALVE Filed July 17, 1929 2 Sheets-Sheet 1 P 1932- o. o. CECCARINII 1,855,623

LIGHT VALVE Filed July 17, 1929 2 Sheets-Sheet 2 Patented Apr. 26, 1932 UNHTED STATES PATENT OFFER OLINDO O. CECCAEINI, OF BEVERLY HILLS, CALIFORNIA, ASSIGNQR TO METRO- GOLDWYN-MAYER CORPORATION, OF CULVER CITY, CALIFORNIA, A CORPORATION OF .NEW YORK LIGHT VALVE Application filed July 17, 1929. Serial ms. 378,907.

This invention relates to a light valve adapt-ed to be used in recording sounds on continuous records. The sounds may be spoken Words, vocal or instrumental music orsome form of noise. The invention particularly relates to an improved light valve adapted to be used in the recording of sounds for subsequent reproduction in proper timed relation With the reproduction of scenes, such as motion p1ctures.

An object of this invention is to disclose and providea light valve having a different response characterlstlc from light valves now in use. Another object of this invention is to disclose andprovide a light valve hav ing a natural period of resonance substantially above the usable range of normal audibility.

Another object is to disclose and provide a light valve which does not discriminate un duly against frequencies of about 7000 cycles or those frequencies which impart a sibilancy to the recorded sound. Another object is to disclose and provide a light valve having a substantially straight line characteristic throughout the major portion of the audible range of frequencies.

Another object is to disclose and provide a light valve which cannot be displaced or fall out of adjustment.

A still further object of the invention is to disclose and provide a light valve in which the spacing or aperture is'maintained subst-antially uniform. Another object is to disclose and provide means for maintaining light valves in spaced relation.

Another object is to disclose and provide a method of raising the natural period of resonance of light valves.

still further object is to disclose and provide a method of reducing the tendency of the light valve ribbons to become displaced or shifted under the action of large signal strengths and vibrations of high amplitude.

.iher objects, uses and advantages of the device embraced by this invention will !become apparent to those skilled in the art, from the following detailed description of one preferred form of the device and of a method of constructing the same. In describing the invention, reference will be had to the appended drawings, in Which:

Fig. 1 is a diagrammatic representation of apparatus Which may be employed in the recordation of sounds, by the use of a light valve adapted to produce a variable density type of record.

Fig. 2 is a. perspective view of a light yalve made in accordance with this inven- Fig. 3 is an enlarged section taken through the light valve illustrated in Fig. 2, the sec tion being taken. along line 3- 3 thereof.

Fig. i is a plan, partly broken away, of a modified form of light" valve.

Fig. 5 is a side elevation, partly broken away, of aportion of the device illustrated in Fig. 4. i

F ig. 6 is an enlarged plan View of one of the supports used in the modified device.

Fig. 7 is a vertical section of the support shown in Fig. 6, the section being taken along line7-7 thereof.

Fig. 8 is a vertical section taken along line 88 of Fig. 7.

The equipment ordinarily employed in sound recording generally comprises a plurality of microphones 1 which are connected to a mixer 2 which controls the gain of the amplifiers for the recording machines, and permits the mixer operator to combine the contributions of the several microphones.

The current then passes throughan amplifier 3, one or more equalizers 4 and attenu ator .5, and then into the recording machines 6. I

The recording machines include a 0011- stant source of light 7, a light valve 8 (through which the signal currents from the amplifiers 3 are passed), and a lens system 9 adapted to focus the image of the light valve ribbons on a film 10. Ordinarily, a condensing lens system 11 is positioned between the constant light 7 and the valve 8 so as to pass a concentrated beam of light through the aperture formed in. the armature of the elec- 2 and 3, comprises a loop of metallic tape 12 suspended in a plane at right angles to a magnetic field. Ordinarily, the tape is made from duralumin and is extremely minute, being about 6 mils wide and 0.3 mils thick. The tape is secured to windlasses 13 and 14 and stretched tightly over a simple elevation 15 which constitutes the armature of an electro-magnet. The windlasses 13 and 14 are connected to the out-put terminals of the recording amplifier, such as for example, the amplifier 3, and generally one of said terminals is grounded.

The tape 12 is maintained under tension by means of a pulley 16 supported on a suitable spring 17. The central portion of the tape or ribbon 12 is supported on insulating bridges 18 and 19 so that the central portion of the tape or ribbon 12 is about 3 mils above the face of the armature 15, and centers over an opening or aperture about 8 mils wide and 250 mils long. In order to produce the desired results, the two portions of the tape or ribbon 12 are separated normally about 2 mils to form a slit or aperture.

When the electro-magnet (of which the hereinabove described light valve assembly is a part) is energized from a battery or other source of direct current,.and the amplifier supplies an oscillating or sine wave current from an oscillator, the two sections of the ribbon or loop 12 open and close in accordance with the current alternations, thereby increasing or decreasing the aperture through which the light is being passed from the light source 7 and condensing lens 11. The volume of light, thus modified, produces a variable density record on the moving film 10, generally the record assuming the form of striations.

The natural frequency of the valve, that is, the natural period of resonance of the tape 12 between the bridges 18 and 19 is, among other things, dependent upon the distance between the supports or bridges 18 and 19 and the mass and tension of the tape or ribbons. For structural purposes and other considerations. light valves of the character described hereinabove have a natural period of resonance at about 7000 cycles. Under these circumstances about 10 milliwatts of A. C. power are required for full modulation of the valve at a frequency remote from resonance, and only about th of this power at the resonant frequency.

A light valve having a natural resonance period of about 7000 cycles, when at such natural frequency, creates or records a note or sound which is the equivalent of a sibilant S.

Furthermore, transients are capable of exciting the valve at the resonant frequency very readily, and, therefore, sound records produced with valves of this character have nssaezs constant presence of sibilant sounds or vibrations. Not only is a valve of this character set into its resonance vibration readily, but furthermore, the amplitude of such vibrations is very much greater than the amplitude of transients and vibrations of lower frequency.

As stated above, it requires but a fraction of the same power to cause the valve to vibrate at maximum amplitude at the resonant frequency that it does at lower frequency, so that with the same amount of power a much greater amplitude is obtained at the resonant frequency than at lower frequencies. Filters or absorbers have been used to oil'- set the excessive response of the light valve at resonant frequency, but no net-work is known at present which will effectively intercept transient impulses.

Furthermore, there is a great tendency for the light valves, or those portions of the tape 12 between the bridges 18 and 19, to become displaced relatively to each other when subjected to a vibration of maximum amplitude, and particularly when such amplitude occurs suddenly. When the valve is displaced and the opening of, say 2 mils, is reduced or occasionally increased to 3 or 4 mils, then the volume, amplitude and distinctness of the record is greatly impaired. When such shifting of the metallic tape 12 takes place during the recording of an orchestration or of dialogue, the entire record is spoiled and must be retaken with a new or readjusted valve.

In remedying the defects of the prior art means have been provided for maintaining the tapes or ribbon 12 in spaced relation with each other over the aperture made in the pole pieces 15. Such means may include any nonconducting material attached to and connecting or in contact with the two loops of the tape 12, the non-conducting spacing member being preferably slidably mounted on the surface of the pole piece 15.

For example, the non-conductive spacing element may comprise a minute piece of fibrous material such as paper or other noneonducting material, such as a pyralin composition 20 placed beneath the loops of the tape 12 and upon the upper continuous surface of the pole pieces 15. The thickness of the member 20 may be from 1 to about 4 mills, but preferably less than the normal height of the tape above the pole pieces. When paper is used for the member 20 a minute piece of cellulose-acetate or other non-conducting cementing fluid is placed on the two loops of the ribbon or tape 12 immediately above the member 20 and a secondary piece of paper, cellulose composition or other nonconducting material 22 then placed upon the loops 12. In this manner, any tendency for the lower member 20 to curl at the edges by been unsatisfactory because of the almost reason of its permeation by the cementing material 21, thereby causing the loops 12 to assume a. position at an angle to the plane of the top of the pole pieces 15, is obviated.

It will be found that the members 20 and 22 will thus be tightly connected to thev loops 12 and form a bridge between the two po1= tions of the loop causing the tapes to retain their desired spacing. The actual or effective length of the ribbons or tapes is shorted to the distance between the pairs of members 20 and 22, even though the lower members 20 do not contact with the upper surfaces of the pole pieces 15. If the lower members 20 are of greater thickness than the normal dis tance between the tape 12 and the top surface of the pole pieces 15, so that the tapes 12 are supported on the surface of the pole pieces by the member 20, then the length is also Shortened.

It has been found that by positioning the members 20 and by forming the spacing and supporting members in a manner similar to that described hereinabove, on the upper sur face of the pole pieces 15 and at a distance of about one-eighth of an inch from the outer edges of the normal pole piece (so as to produce a length of about 0.8 inches), the nat ural. frequency orfundamental of the tape is increased to between 8500 and 10,000 cycles. A valve made as described hereinabove is, therefore, incapable of responding abnormally to a frequency of 7000 cycles and, therefore, improved valves made in accordance with this invention do not produce the undesirable sibilant sound or note which destroys the distinctness of vocal music and recordings.

The natural resonance or resonant frecuency of 7000 cycles is within the useful and esired range of the frequencies, and for this reason a valve which can be readily excited and caused to oscillate to this frequencyis undesirable. Natural frequencies of between 8500 and 10,000 cycles are not within this useful or desired range. F or this reason the im proved valve embraced by this invention is particularly useful.

Furthermore, inasmuch as the two loops of the ribbon or tape 12 are maintained in spaced relation by the positive grip of the members 20 and 22 upon the members 12, the spacing of the two portions of the loop 12 is maintained even. though the tape is subjected'to strong. signal currents and to a vibration of maximum amplitude. Bynot'cementing or affixing the member 20 to the top of they pole piece 15, the function of the tensioning de- Vice such as the pulley 16'and the spring 17,

is not impaired and any actual elongation or longitudinal displacement which occurs durin g the operation of the valve compensated for by the tensioning device 17/ The modified form of device shown in Fig. l includes a modified type of bridge and a new and novel placement of the ribbon or tape. The ribbon or tape preferably is attached at one end to a Windlass such'as the Windlass 13, then passes over a bridge 23 and behind a stop made of non-conducting material 24c. The tape then passes across the top of the pole piece 15, and comes into abutting relation with another stop or spacing member 25, thesai d spacing member 25 being in alinement with the spacing member 24 and in a plane passing through the aperture formed in the pole piece 15. The tape 12 is then passed over a pulley 16 which may be either mounted on a vertical spindle or on a spindle inclined to the vertical plane, said spindle preferably forming a part of a spring or other tensioning device 17 The return portion of the tape 12, indicated at 26, then preferably passes under the tape 12 and crosses the tape 12 in rising over the bridge 27, so as to come into abutting relation with the free side of the spacing member 25. The tape then travels over the top of the pole piece 15, comes into abutting relation with the spacing member 2a, and crosses over the tape 12, the end of the tape 28 being attached to a suitable contact or Windlass 14-.

By thus closing the two ends of the loop formed by the ribbon or tape 12, the central portion of the loop is separated by the members 24: and 25 which are of precisely the required distance which it is desired to keep the loop portions separated.

Electrical contact between the two portions of the loop formed by the ribbon or tape 12 is precluded by forming the bridge members 23 and 27 in such manner that one portion of the loop is maintained above the other portion, the bridge being composed of insulating material such as a phenol condensation product. It has been found that by constructing the light valve as described hereinabove, not only is the spacing of the valves maintained substantially constant, but in addition better recordings are produced and the tendency for the tape or ribbon 12 to vibrate at a natural frequency capable of creating unsatisfactory results has been eliminated to a large extent.

It is to be understood that the invention is not limited to the particular method of constructing the light valves described here inabove, nor to the employment of the materials specified in detail, but includes all such changes and modifications as come within the sco e of the appended claims. The invention, in general, relates to means for maintainingthe light valves in spaced relation and to the provision of a light "alve incapable of being easily displaced and/or vibrating at an undesirable audible fre quency.

lVhat I claim is:

1. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, an aperture in said armature, non-conducting bridges adapted to support a metallic tape over sald armature and over said aperture thereln, a

metallic tape loop suspended over said armature, and a pair of members spaced longitudinally of said taped loop for maintaining adjoining portions of said tape loop in minimum spaced relation with each other.

2. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, an a )erture in said armature, non-conducting ridges adapted to support a metallic tape oversaid armature and over said aperture therein, a metallic tape loop suspended over said armature, means for maintaining said tape loop under tension, and a pair of members spaced longitudinally of said taped loop for maintaining adjoining portions of said tape loop in minimumspaced relation with each other.

3. An improved light valve adapted to be activated by an oscillating current, comprising an armature, an aperture in said armature, non-conducting bridges adapted to support a metallic tape over said armature and over said aperture theref n, a metallic tape loop supported by said bridges and suspended over said armature, and means carried by each of the bridges for maintaining adjoining portions of said tape loop in minimum spaced relation with each other.

l. An improved light valve adapted to be activated by an oscillatingcurrent, comprising an armature, an aperture in said armature, non-conducting bridges adapted to support a metallic tape over said armature and over said aperture therein, a metallic tape loop suspended over said armature, and a pair of non-conducting members spaced longitu- A dinally of said taped loop and connecting adjacent portions of said tape loop over said armature in spaced relation with each other.

An improved light valve adapted to be activated by an oscillating current, comprising an armature, an aperture in said armature, non'conducting bridges adapted to support a metallic tape over said armature and aperture, a metallic tape loop suspend-ed over said armature. means for maintaining said tape loop under tension, and a pair of nonconducting members spaced longitudinally of said taped loop and connecting adjacent portions of said tape loop over sa d pole pieces in spaced relation with each other.

6. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, pole pieces carried by the armature, an aperturebetween said pole pieces, non-conducting bridges carried by said armature adapted to support a metallic tape above said pole pieces andaperture, a metallic tape loop supported by said bridges and supended over said pole pieces, and a pair of non-conducting members spaced longitudinally of said tape loop and possess connecting adjacent portions of said tape loop between said bridges and over said pole pieces in spaced relation with each other whereby that portion of the taped loop between said spaced members is normally maintained in parallel alignment.

7. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, pole pieces carried by said armature, an aperture between said pole pieces, non-conducting bridges carried by said armature adapted to support a metallic tape above said pole pieces and aperture, a metallic tape loop supportedby said bridges and suspended over said pole pieces, and a pair of non-conducting members spaced longitudinally of said taped loop and connecting adjacent portions of said tape loop between said bridges and over said pole pieces in spaced relation with each other, said means being detached from said pole pieces and bridges.

8. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, pole pieces carried by said armatu an aperture tween said pole pieces, non-conducting bridges carried by said armature adapted to support a metallic tape above said pole pieces and aperture, a metallic tape loop supported by said bridges and suspended over said pole pieces, and non-conducting means connecting adjacent portions of said tape loop between said bridges and over said pole pieces in minimum spaced relation with each other, said means comprising upper and lower members extending over adjacent loop portions and connected thereto by a nonconducting cementing material.

9. An improved light valve adapted to be activated by an oscillating current, comprising in combinationan armature, pole pieces carried by said armature, an aperture between said pole pieces, non-conducting bridges carried by said armature adapted to support a metallic tape above said pole pieces and aperture, a metallic tape loop supported by said bridges and suspended ov r said pole pieces, and non-conducting means connecting adjacent portions of said tape between said bridges and over said pole pieces in spaced relation with each other, said means being detached from said pole pieces and bridges and comprising upper and lower members extending over adjacent loop portionsand connected thereto by a non-conducting eementing material.

10. An improved light valve adapted to be activated by an oscillatingcurrent, comprising an armature, an aperture in said'armature, non-conducting bridges adapted to support a metallic tape over said armature and over said aperture therein, a metallic tape loop suspended over said armature, means for maintaining said tape loop under tension,

Lemmas and a pair of members spaced longitudinally of said taped loop for maintaining adjacent portions of said tape loop in minimum spaced relation, adjacent sections of said loop 5 being substantially closed so as to maintain said sections in contact with said spacing means.

11. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, an aperture in said armature, a pair of spaced non-conducting bridges adapted to support a metallic tape over said armature and aperture, a metallic tape loop supported by said bridges and suspended over said armature, means for maintaining said tape loop under tension, and means carried by each of the bridges for maintaining adjoining sections of said tape loop in minimum spaced relation with each other, adjoining sections of said loop being substantially closed externally of said bridges so as to maintain said sections in contact with said spacing means.

12. An improved light valve adapted tobe activated by an oscillating current, comprising an armature, an aperture in said armature, non-conducting bridges adapted to support a metallic tape over said armature and over said aperture therein, a metallic tape loop suspended over said armature, means for maintaining said tape loop under tension, a pair of members spaced longitudinally of said taped loop for maintaining adjoining sections of said tape loop in minimum spaced relation with each other, adjoining sections of said loop being substantially closed so as to maintain said sec tions in contact with said spacing means, and means for maintaining the closed portions of said loop out of electrical contact with each other.

13. An improved light valve adapted to be activated by an oscillating current, comprising in combination an armature, an aperture in said armature, a pair of spaced non-conducting bridges adapted to support a metallic tape over said armature and aper ture, a metallic tape loop supported by said bridges and suspended over said armature, means for maintaining said tape loop under tension, means carried by each of the bridges for maintaining adjoining sections of said tape loop in minimum spaced relation with each other, adjoining sections of said loop being substantially closed externally of said bridges so as to maintain said sections in contact with said spacing means, and means for maintaining the closed portions of said loop out of electrical contact with each other.

14. An improved light valve adapted to v aperture in said armature, a pair of spaced non-conducting bridges adapted to support a metallic tape over said armature and aperture, a metallic tape loop supported by said bridges and suspended over said armature, means for maintaining said tape loop under tension, and means carried by each of the bridges for maintaining adjoining sections,

of said tape loop in minimum spaced relation with each other, adjoining sections of said loop being substantially closed externally of said bridges so as to maintain said sections in contact with said spacing means, said bridges being adapted to maintain closed portions of said loop out of electrical contact with each other.

15. In a light valve, the combination of substantially parallel conductors positioned in a magnetic field and a pair of non-conducting means spaced longitudinally of said conductors and connecting said conductors, said means being adapted to maintain said conductors for a portion of their length in minimum spaced relation with each other.

Signed at Culver City, Calif., this 6th day of July, 1929.

' OLINDO O. CECGARINI. 

